A ghost is troubling the fellows of Peterhouse, Cambridge. Elaine Williams reports

One evening last spring one of the fellows of Peterhouse, Cambridge, was hosting a private dinner in a parlour above the Combination Room.

The room was candlelit, as dinners and meetings at Peterhouse always are - even the governing body meets by candlelight - and a soft, flickering glow gave warmth to the meal in this, the oldest of the Cambridge Colleges.

At 8.45pm two members of the butler's pantry staff, who were serving the dinner guests, descended the spiral staircase that connects the upper parlour to the Combination Room, a 13th-century oak-panelled chamber, to fetch the hot plates. They turned on the low wall lights but, as they were leaving the room, they froze. Before them was a figure, floating above the ground. As they watched, it moved slowly towards a window to their right and disappeared.

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Badly shaken, the servers notified the college's dean. More stories emerged. Other members of staff, both from the butler's pantry and the kitchen, relayed tales of insistent knocking coming from behind the panelling in the Combination Room, accompanied by a sudden drop in temperature. So "real" was the knocking that the butler went down to the cellars to try to discover the source. All of the stories were entered into the college record, but nothing else happened.

Last month, however, when the dean was at High Table for dinner after a governing body meeting in the Combination Room, he was approached by a member of the pantry staff who blurted: "It's happening again." The dean was in a quandary. To leave High Table would have caused a scene and, in any case, the master of the college was a hardline scientist. The dean told the server that he would speak to him later. But after only five minutes the man was back. The knocking had started as well.

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The dean saw he had no choice. He left High Table to enter the Combination Room, where the head butler was on the floor whispering, "It's fading, it's fading." Once again, it seems, the apparition had moved slowly over to the window and disappeared, followed by wild knocking around the room. The servers pointed out that the time of its appearance was the same, for, although the clock read 7.45pm, the hour had gone back for the winter.

The dean summoned the diocesan exorcist. The men who had seen the ghost were sensible, straightforward teetotallers. They were not tricksters. The head butler was down-to-earth, the kind of man who would be more than ready to accept a natural explanation for the Peterhouse disturbance.

Knockings, explained the exorcist, could be rats in the wainscot or water pipes, but they could also be caused by psychic disorder. Troubled persons can trigger such effects in a room. Knockings require only a simple service, but sightings of ghosts are a different matter. Restless souls, not departed, require a requiem mass of the whole family - in the case of Peterhouse the whole body of fellows and domestic staff. Difficult enough getting them together for a Christmas party, but for a mass for someone who died long ago? The advice left the college at a loss as to what to do.

The fellows are inclined to wait and see what happens next. They may not have to wait long. Only a fortnight ago the bursar, who is a college fellow, entered the Combination Room late one night to take fruit back to his lodgings. Bending over the fruit bowl he too heard the knocking and was aware of a cold presence behind him. Apparently this is what he told the butler's pantry staff, but on an approach by the dean he suggested that the noise could have been caused by water in the pipes.

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There is much speculation among the fellows. Who could this presence be and why now? The dean has been investigating. In the book of Cambridge College Ghosts there is a story of a bursar, Francis Dawes, who hanged himself in the late 18th century after shenanigans over the election of a master.

The book says that he used the bell rope in the Peterhouse chapel vestibule. But the dean thinks otherwise. College records say Dawes was hanged by a bell rope but do not specify the chapel. There is a bell rope outside the Combination Room and a spiral staircase the beleaguered bursar could easily have thrown himself off. Until William Morris re-designed the Combination Room, putting in the window the "presence" moves towards, there would have been a door into the garden or through to the staircase.

Peterhouse is no stranger to exorcisms. One performed by a former dean was due to a dark presence sitting in the corner of the old quad overlooking the graveyard of St Mary-the-Virgin next door. The other was due to a poltergeist in a student's room in an 18th-century terraced block.

The present dean is all at sea. As a philosophical theologian his work is on religious doctrine. There is no systematic theology that deals with ghosts, but he does have a new name - the Ghostbuster.

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